One type of motorless mass flowmeter employs a turbine driven by flow of fluid therethrough to supply torque to a drum housing an impeller at which mass of the fluid is measured.
In such mass flowmeters, the impeller may be arranged concentrically within the drum, the impeller being rotationally coupled to the drum by way of a torsion spring that allows relative rotation against the bias of the torsion spring. As the drum is made to rotate in rigid accompaniment to rotation of the turbine, impingement of flowing fluid mass on the vanes of the impeller causes rotation of the impeller to lag behind rotation of the drum against the bias of the torsion spring. By mounting magnets on the drum and the impeller, and using pickup coils to detect passage of the magnets, fluid mass can be determined as a function of the difference in time between the rotational position of the drum and the rotational position of the impeller.
Such a mass flowmeter might, for example, be used in an aircraft to measure fuel consumption. In such applications it is usually preferred for accurate measurement that the mass flowmeter be arranged in-line between the fuel supply and the engine in such fashion that all fuel consumed by the aircraft engine passes through the mass flowmeter. Alternatively, the mass flowmeter might be arranged in the fuel line in such manner that a known fraction of the fuel consumed by the engine passes through the mass flowmeter. No matter how the mass flowmeter is installed, however, it is to be expected that the mass flowmeter will be exposed to varying fuel flow rates depending on the rate of fuel consumption by the engine.
The mechanical system of such a mass flowmeter will typically have a safe or preferred range of rotational velocities within which various drags and other mechanical noise are comparatively small and there is good dynamic stability on the one hand, but there is also little danger of excessive wear or damage to the various bearings and other mechanical components on the other. In particular, the torsion spring typically employed between impeller and drum will generally have a safe or preferred range of torsional deflections, and thus a safe or preferred range of rotational velocities of the mass flowmeter, over which it can operate. Furthermore, the electronic detection system responsible for inductively detecting start and stop pulses produced by passage of drum and impeller magnets in such a mass flowmeter will similarly typically have a preferred range of rotational velocities within which detection is carried out most satisfactorily. Moreover, with respect to the fluid dynamic system of the mass flowmeter, while many of the components of the mass flowmeter may be designed to handle a wide variety of flow rates, it is difficult to design a turbine that is sensitive enough to provide adequate torque to the impeller at low flow rates yet robust enough not to exhibit poor performance at high flow rates. With conventional mass flowmeter turbines, it is possible, for example, that at high flow rates, back-pressure from the mass flowmeter will interfere with flow of fuel to the engine or otherwise adversely impact the fluid system in which the mass flowmeter is employed.
There is therefore a need for a motorless mass flowmeter having a turbine subassembly possessing a bypass valve system for regulation of pressure and/or rotational velocity. It is furthermore desired that such a bypass valve system permit the mass flowmeter to be sensitive enough to operate at low flow rates, yet be robust enough to operate without adverse effect at high flow rates. It is moreover desired that the turbine subassembly of such a motorless mass flowmeter be capable of causing an impeller to rotate at rotational velocities within a preferred range without production of adverse phenomena such as high back-pressure over a wide range of flow rates.
Furthermore, conventional mass flowmeter bypass valves may be expensive and/or difficult to manufacture. There is therefore a need for a mass flowmeter bypass valve design that is inexpensive and easy to manufacture. For example, a laminated bypass valve structure easily manufacturable from layers of stamped or punched sheet metal is desired.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.